Cycle wheel rim and method of manufacture

ABSTRACT

The invention includes a rim for a cycle wheel having a U-shaped radial cross section, with two lateral flanges located on opposite sides of a median plane of the rim and each demarcated by an outer surface facing away from the median plane, on the one hand, and a bridge connecting the flanges and comprising an outer surface facing toward the axis of rotation of the wheel, on the other hand. At least one median zone of the outer surface of the bridge, which has a transverse width measured perpendicular to the median plane and greater than 4 mm, is machined over the entire circumference of the rim.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon French Patent Application No. 12/00021,filed Jan. 4, 2012, the disclosure of which is hereby incorporated byreference thereto in its entirety, and the priority of which is claimedunder 35 U.S.C. §119.

BACKGROUND

1. Field of the Invention

The invention relates to a rim for a cycle wheel, and a method formanufacturing such a rim.

2. Background Information

Conventionally, a cycle wheel rim is annular and has a U-shaped radialcross section, with two lateral flanges that are generally perpendicularto the axis of rotation of the wheel and a bridge that connects thelateral flanges and is oriented so as to be opposite the axis ofrotation of the wheel. In the case of a spoked wheel, the spokes aregenerally fastened to the bridge of the rim.

To manufacture a cycle wheel rim, it is known to make a rectilinearsection by extruding or spinning a metal alloy, such as an aluminumalloy, for example, and then bending the section into an annular shape.The ends of the rim are then connected to one another, for example bywelding.

It is advantageous to produce a lightweight rim, in order to optimizethe performance of the cyclist, while maintaining sufficient rigidityand strength to avoid breakage.

The extrusion process requires minimum wall thicknesses, for the yieldstress increases significantly when the thickness decreases and thecharacteristics of the alloy and the spinning speed increase. Thus, foralloys that are typically used in the manufacture of rims, it is veryrisky to go below thicknesses of 0.85 mm, as doing so may quickly breakthe extrusion die.

In addition, the bending of a section causes significant plasticdeformations, particularly in the zones that are away from the center ofgravity of the cross section. These substantial plastic deformationscause dislocations of the grains of the material which, in turn, canresult in a surface finish known as “orange peel,” which is oftenconsidered unsightly.

Furthermore, overly thin lateral walls also generate local buckling ofthe walls of the section during bending, when subject to overly highcompressive deformations.

To overcome the aforementioned drawbacks, the document FR-A-2 727 355proposes to make a rim by extruding a rectilinear section havingsufficient thickness to prevent the extrusion from causing defects inthe material. The section is then bent, and it does not change and doesnot buckle due to its thickness. To reduce the weight of the rim, therim is then immersed in an aggressive chemical bath which attacks thematerial and decreases its thickness. This manufacturing method isrelatively cumbersome to implement and, although the surface finish doesbecome uniform, it remains quite rough.

Similarly, the document U.S. Pat. No. 6,961,999 proposes extruding andbending a sufficiently thick section in order not to cause manufacturingdefects. The lateral flanges of the rim are then machined to reducetheir thickness and to decrease the weight of the rim. The documentEP-A-0 579 525 also proposes machining the lateral flanges of the rimafter extrusion and bending of the section. Reducing the weight of therim is not optimal because the bridge of the rim retains its initialthickness.

It is also known, from the documents EP-A-1 084 868 and EP-A-1 491 362,to machine the section after bending, both in the area of the bridge andin the area of the lateral flanges of the rim, and only on certainportions of the circumference of the rim. The machining istime-intensive and it is complex to implement, because it requires theuse of a five-axis machine.

When it is desired to produce a plurality of rims having variousgeometries, for example with respect to the number of spokes, thelocation of the spoke fastening zones, or the thickness of the rim, allof these methods require a modification of the manufacturing parameters,in particular with respect to the machining for material removal and/orchemical milling. This leads to additional development costs and doesnot standardize the manufacturing method.

SUMMARY

The foregoing are drawbacks that the present invention overcomes,particularly by providing a cycle wheel rim and a method formanufacturing such a rim, which makes it possible to reduce the weightof the rim while optimizing rigidity. In addition, the rim according tothe invention can be manufactured quickly, and the manufacturing methodprevents the occurrence of defects during the extrusion and bending ofthe section.

The useful life of rims is often limited by the appearance of cracks inthe spoke fastening zone. Once they occur, such cracks propagate veryquickly in the spinning direction, quickly causing a rupture of thebridge. This well-known fatigue phenomenon is due to the numerous loadcycles to which the spokes are subjected at each turn of the wheel, onthe one hand, and it is also accelerated by small surface defects whichtypically are longitudinal striations caused by friction of the metal inthe die during the spinning operation, on the other hand. The inventiontherefore also optimizes the fatigue strength of the rim by locallyreinforcing the fastening of the spoke, but also by improving thesurface finish in order to eliminate or delay the initiation of fatiguecracks.

To these ends, the invention provides a cycle wheel rim and a wheelhaving a U-shaped radial cross section, with two lateral flanges locatedon opposite sides of a median plane of the rim and each demarcated by anouter surface facing away from the median plane, on the one hand, and abridge connecting the flanges and comprising an outer surface facingtoward an axis rotation of the wheel, on the other hand. At least onemedian zone of the outer surface of the bridge, having a transversewidth measured perpendicular to the median plane and greater than 4 mm,is machined on at least 95% of the circumference of the rim.

Due to the invention, the bridge of the rim is machined at leastpartially on the entire circumference of the rim, including in the areaof the spoke fastening zones. Thus, the weight of the rim is reduced. Inaddition, the machining improves the surface finish of the bridge byeliminating the defects resulting from spinning or bending the section,thereby improving the fatigue strength. In the various embodiments whichare described below, the machining is done on the entire circumferenceof the rim. In other embodiments not described in detail below, whichare also encompassed by the invention, the machining is carried out onalmost the entire circumference. In this case, at least 95%, or even97%, of the circumference is machined. This configuration may beselected if it is desired, for example, to produce an unbalance tocounterbalance the weight of the splice bar of a sleeved rim and/or ofthe inflation valve. In a particular embodiment, even in the case inwhich only 95% of the circumference of the rim is machined, it isnecessary to ensure that all of the spoke fastening zones are machined.

According to advantageous but not essential aspects of the invention,such a rim may incorporate one or more of the following characteristics,taken in any technically permissible combination:

-   -   The outer surface of the bridge is machined in its entirety,        over the entire circumference of the rim.    -   The rim has an outer surface facing outward of the rim and        including both the outer surface of the bridge and at least a        portion of the outer surface of the flanges, which is connected        to the outer surface of the bridge. The outer surface of the rim        is machined in its entirety over the entire circumference of the        rim.    -   The outer surface of the rim comprises the entire outer surface        of the flanges.    -   The rim is divided into a plurality of zones which divide the        circumference of the rim into angular sectors, the zones        including:        -   transmission zones located around the zones of attachment of            the spokes of the wheel; and        -   intermediate zones located between the transmission zones.            In the area of the transmission zones, the thickness of the            bridge, measured in the median plane of the rim, is equal to            a maximum thickness. In the area of the intermediate zones,            the thickness of the bridge is equal to a minimum thickness            that is less than the maximum thickness.    -   The maximum thickness of the bridge is greater than 1.6 mm,        preferably greater than 2 mm.    -   The minimum thickness of the bridge is less than 0.8 mm or, in a        particular embodiment, less than 0.65 mm.    -   The zones further include transition zones each located between        a transmission zone and an intermediate zone. In the area of the        transition zones, the thickness of the bridge is equal to an        intermediate thickness, which varies progressively between the        minimum thickness and maximum thickness of the bridge.    -   In a radial cross section of the rim, a radius of curvature of        the bridge is less than 15 mm or, in a particular embodiment,        less than 10 mm.    -   The bridge includes internally threaded cylindrical bushings for        fastening the spokes of the wheel, and the bushings are made        unitary with the rim.    -   The flanges each define a planar braking surface, provided to        cooperate with a brake pad. A height of at least one braking        surface, measured radially, is greater in the area of the        transmission zones than in the area of the intermediate zones.

The invention also relates to a method for manufacturing a cycle wheelrim, comprising:

-   -   extruding a rectilinear section, such section comprising two        lateral flanges located on opposite sides of a median plane of        the rim and each demarcated by an outer surface facing away from        the median plane, on the one hand, and a bridge connecting the        flanges and demarcated by an outer surface facing toward an axis        of rotation of the wheel, on the other hand;    -   bending the section to form at least one hoop, or ring;    -   assembling the ends of the hoop formed from the section by        affixing each to the other;    -   drilling holes in the bridge for fastening the spokes of the        wheel.

According to the invention, the method further comprises machining,carried out after the drilling, whereby, at least one median zone of theouter surface of the bridge, which has a transverse width measuredperpendicular to the median plane and greater than 4 mm, over the entirecircumference of the rim.

The manufacturing method is standardized, that is to say, it is possibleto easily manufacture rims of various geometries from the same section,without the need to change the tools provided for the extruding,bending, and machining. For example, for the manufacture of a line ofrims, various front and rear wheel rims can be made from the samesection and using the same machining tools.

Fatigue cracks generally occur in the area of the bridge of the rim,around the spoke fastening zones. If the strength of a rim made by sucha method proves to be insufficient, the thickness of the bridge of therim can easily be increased, at least in the area of certain zones ofthe circumference of the rim, by keeping the initial tools and byvarying the geometric parameters of the machining. For example, if therim is machined with a milling cutter having a concave profile, itsuffices to shift the milling cutter toward the axis of rotation of therim to increase the thickness of its walls. Thus, the rim developmentcosts are reduced.

According to advantageous but not essential aspects of the invention,such a manufacturing method may incorporate one or more of the followingcharacteristics, taken in any technically permissible combinations:

-   -   The outer surface of the bridge is machined in its entirety,        over the entire circumference of the rim.    -   During machining, an outer surface of the rim, facing outward of        the rim and including both the outer surface of the bridge and        at least a portion of the outer surface of the flanges connected        to the outer surface of the bridge, is machined in its entirety,        over the entire circumference of the rim.    -   Machining is carried out using a milling cutter having a concave        profile and enabling the bridge and at least a portion of the        flanges adjoining the bridge to be machined simultaneously in a        radial plane.    -   At the end of extruding, a radius of curvature of the outer        surface of the bridge of the section, measured in a radial plane        of the rim, is greater than 20 mm. At the end of machining, a        radius of curvature of the outer surface of the bridge of the        rim is less than 15 mm or, in a particular embodiment, less than        10 mm.    -   At the end of extruding, a thickness of the bridge of the        section is greater than 1.6 mm or, in a particular embodiment,        greater than 1.9 mm.    -   A ratio, whose denominator is a thickness of the bridge of the        section, measured at the end of extruding, and whose numerator        is a thickness of the bridge of the rim, measured at the end of        machining, is less than 90%.    -   During drilling, holes and bushings for fastening the spokes are        made simultaneously by flow drilling the bridge, without        cutting.    -   A minimum removed material thickness, equal to the difference        between the thickness of the bridge of the section, measured at        the end of extruding, and the minimum thickness of the bridge of        the rim, measured at the end of machining and considered over        the entire circumference of the rim, is greater than 0.1 mm or,        in a particular embodiment, greater than 0.3 mm.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood upon reading the followingdescription of a cycle wheel rim and of a method for manufacturing sucha rim in accordance with its principle, given solely by way of exampleand in reference to the annexed drawings, in which:

FIG. 1 is a perspective view of a cycle wheel shown without the tire andincluding a rim according to the invention;

FIG. 2 is a side view of the detail II of FIG. 1;

FIGS. 3, 4, and 5 are radial cross sections along the lines IV-IV, andV-V of FIG. 2, the spokes being omitted in FIG. 5 for clarity of thedrawing;

FIG. 6 is a transverse cross section of a section from which the rim ismade;

FIG. 7 is a perspective view of an unworn rim brake element, used tobrake the wheel of FIG. 1 and shown bearing against the rim, which ispartially shown;

FIG. 8 is a cross section along the plane P8 of FIG. 7;

FIG. 9 is a view, similar to FIG. 7, of a worn out rim brake element;

FIG. 10 is a block diagram of a method for manufacturing the rim;

FIG. 11 is a view, similar to FIG. 2, of a rim according to a secondembodiment of the invention;

FIGS. 12-15 are cross sections along the lines XII-XII, XIII-XIII,XIV-XIV, and XV-XV of FIG. 11, the spokes being omitted in FIGS. 12, 13,and 15 for clarity of the drawings;

FIG. 16 is a schematic diagram showing two cross sections of a rimaccording to a third embodiment of the invention, overlaid with a crosssection of a section from which this rim is made;

FIG. 17 is a perspective view of a milling cutter used during themanufacture of the rim of FIG. 1;

FIG. 18 is a transverse cross section of a section from which a rim ismanufactured according to a fourth embodiment of the invention;

FIG. 19 is a radial cross section of the rim according to the fourthembodiment of the invention;

FIG. 20 is a schematic diagram showing three cross sections of the rimof FIG. 19, overlaid with the cross section of the section of FIG. 18;and

FIG. 21 is a view, on a larger scale, of the detail XXI of FIG. 20.

DETAILED DESCRIPTION

FIG. 1 shows a bicycle rear wheel 1, without a tire mounted thereon. Thewheel 1 comprises two sets 4 a, 4 b of spokes 4 a 1, 4 a 2, 4 b 1mounted on a rim 3. The spoke sets 4 a, 4 b are connected to a hub 2 ofthe wheel 1, which comprises a hub body 21 extending along an axis ofrotation X of the wheel 1. A freewheel mechanism 22 is connected to oneend of the hub body 21 which supports the spoke set 4 a, and the otherend of the hub body 21 supports the spoke set 4 b. The freewheelmechanism 22 is provided to be assembled with a sprocket cassette (notshown).

When a cyclist pedals in the forward direction, the cyclist rotates thewheel 1 about the axis of rotation X through the sprocket cassette andthe freewheel mechanism 22 in a direction designated by the arrow F inFIG. 1.

The spoke set 4 a comprises driving spokes 4 a 2, which pull on the rim3 when the cyclist pedals, and non-driving spokes 4 a 1, or pushingspokes, which tend to relax when the cyclist pedals. The spoke set 4 ais the driving set; its spokes 4 a 1 and 4 a 2 are fastened on the sideof the hub body 21 which carries the freewheel mechanism 22 and receivesthe torque resulting from the pedaling force from the cyclist.Conversely, the spoke set 4 b is the driven set.

As shown in FIGS. 3 to 5, the radial cross section of the rim 3, is inthe form of a hollow box, or having a U-shape, with a transverse wall 7,or bridge, connecting the two vertical arms of the “U”. The expression“radial cross section” refers herein to a cross section in a plane P4passing through the axis X, oriented along a radial direction. The rim 3comprises two lateral flanges 5 a and 5 b, or sidewalls, and a curved,or arcuate, bridge 6 connecting the flanges/sidewalls 5 a and 5 b to oneanother and forming the curved portion of the U-shaped cross section.The bridge 6 is located on the side of the axis of rotation X, or facesthe axis of rotation, and the transverse wall 7 is located on the sideof the tire, or faces the tire. Although the transverse wall 7 could bereferred to as a bridge or upper bridge (and bridge 6, a lower bridge),the wall 7 is referred to herein as a transverse wall. The rim 3 thusdemarcates an inner volume V. The convex side of the bridge 6 isoriented so as to be opposite the axis X, and the concave side of thebridge 6 is oriented toward the tire. The transverse wall 7 is generallyperpendicular to the flanges 5 a and 5 b and connects the flanges 5 aand 5 b to one another, opposite the bridge 6. On the side opposite thebridge 6, the flanges 5 a and 5 b are each provided with an L-shapedhook 51 a and 51 b, provided for fastening a tire, not shown, to the rim3. The hooks 51 a and 51 b project outward of the box formed by the rim3. The box shape of the rim 3 is demarcated by the flanges 5 a and 5 b,the bridge 6, and the transverse wall 7.

The rim 3 is provided to be used with a rim brake system comprising twobraking elements 8, one of which is shown in FIG. 7; such brakingelements 8 are mounted on a stirrup attached to the frame of the cycle.Each braking element 8 comprises a pad 81 mounted on a support element82 and extends longitudinally along an axis X8 which, during use, islocally tangent to a circumferential direction of the rim 3. In otherwords, during use, the axis X8 extends along an orthoradial direction ofthe rim 3. Each pad has a decreasing width L8, between the portion 84fixed to the support 82 and the friction surface S8 in the form of aring section, which comes into contact with braking surfaces S5 a and S5b of the rim 3 during braking. The width L8 is measured perpendicular tothe axis X8 and parallel to the surface S8.

The braking surfaces S5 a and S5 b are defined outside of the volume Vby the hooks 51 a and 51 b and a portion of the flanges 5 a and 5 badjoining the hooks 51 a and 51 b. The surfaces S5 a and S5 b are flatand perpendicular to the axis X.

Notable is a median plane P of the wheel 1, perpendicular to the axis X.The median plane P passes between the flanges 5 a and 5 b and betweenthe hooks 51 a and 51 b, at equal distances therefrom. Thus, the flanges5 a and 5 b are located on opposite sides of the median plane P.

Also notable is the height h5 of the braking surfaces S5 a and S5 b,measured parallel to the plane P, along a radial direction R of thewheel 1. See FIG. 3.

The peripheral ends of the spokes 4 a 1, 4 a 2, 4 b 1 are equipped withthreaded heads 40 attached to the bridge 6 of the rim 3. The bridge 6comprises holes 41, the edges of which are extended inward of the innervolume V by a generally cylindrical bushing 42. The bushings 42 areinternally threaded for threaded engagement with the heads 40.

A valve hole 43 (see FIG. 1) is made through the bridge 6 and thetransverse wall 7. When a tire is mounted on the rim 3, the tire valveis inserted into the valve hole 43 and projects outward from the rim 3.

The transverse wall 7 is provided with a locating member 71, such as aridge, that is offset relative to the plane P. The locating member 71makes it possible to identify the right side and the left side of therim 3, to facilitate the mounting of the spokes 4 a 1, 4 a 2, 4 b 1.

The bridge 6 has a thickness e6 measured along the radial direction R,in the plane P and perpendicular to the axis X.

The rim 3 is divided into a plurality of zones Z1, Z2, Z3 a 1, Z3 a 2,Z3 b 1, which divide the circumference of the rim 3 into a plurality ofangular sectors. The transmission zones Z3 a 1, Z3 a 2, Z3 b 1 arelocated around holes 41 where the spokes 4 a 1, 4 a 2, 4 b 1 aremounted. Two transition zones Z2 are located on both sides of eachtransmission zone Z3 a 1, Z3 a 2, Z3 b 1. The intermediate zones Z1 arelocated between the transition zones Z2 and are farther away from theholes 41 than the zones Z2, Z3 a 1, Z3 a 2, Z3 b 1. Thus, eachtransition zone Z2 is located between a transmission zone Z3 a 1, Z3 a2, Z3 b 1 and an intermediate zone Z1.

During use, the transmission zones Z3 a 1, Z3 a 2, Z3 b 1 are subject tomechanical stresses of relatively high intensity because it is in thisarea that the force produced by the cyclist is transmitted to the rim 3.The transition zones Z2 are subject to mechanical stresses of averageintensity because they are adjacent the transmission zones Z3 a 1, Z3 a2, Z3 b 1. The intermediate zones Z1 are subject to relatively lowmechanical stresses because they are away from the transmission zones Z3a 1, Z3 a 2, Z3 b 1.

The greater the thickness e6 of the bridge 6, the stronger and heavierthe rim 3 will be. Conversely, the smaller the thickness e6 of thebridge 6, the weaker and lighter the rim 3 will be. To obtain a rim 3with satisfactory mechanical strength and reduced weight, the thicknesse6 is adapted as a function of the mechanical stresses withstood by thevarious zones Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1.

In the area of the intermediate zones Z1, the thickness e6 is equal to aminimum thickness e6min. The thickness e6min is less than 0.8 mm or, ina particular embodiment, less than 0.65 mm.

In the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, thethickness e6 is equal to a maximum thickness e6max, greater than theminimum thickness e6min. The thickness e6max is greater than 1.6 mm or,in a particular embodiment, greater than 2.0 mm.

Moreover, the intensity of the mechanical forces transmitted to the rim3 by the spokes 4 a 1, 4 a 2, 4 b 1 is not the same, depending uponwhether the spoke 4 a 1, 4 a 2, or 4 b 1 is part of a driving or drivenset 4 a or 4 b, and whether the spoke is a driving spoke 4 a 2 or anon-driving spoke 4 a 1. In addition, the intensity of the forcestransmitted is not the same for the wheel 1, which is the drive wheel ofthe cycle, and for the front wheel of the cycle, not shown.

Thus, the thickness e6max is not the same for each transmission zone Z3a 1, Z3 a 2, Z3 b 1. The thickness e6max of the transmission zones Z3 a1, in which the driving spokes 4 a 2 are fastened, is greater than thethickness e6max of the transmission zones Z3 a 2, in which thenon-driving spokes 4 a 1 are fastened. The thickness e6max of thetransmission zones Z3 b 1, in which the driving spoke set 4 a isfastened, is greater than the thickness e6max of the transmission zonesZ3 a 2, in which the driven spoke set 4 b is attached. The thickness e6of the drive wheel 1 of the cycle, in a particular embodiment, isgreater than or equal to the thickness e6 of the front wheel of thecycle.

Optionally, the flanges 5 a and 5 b can be locally thicker in the areaof the transmission zones Z3 a 1, Z3 a 2, Z3 b 1 and in the area of theconnecting zones Z2 than in the area of the intermediate zones Z1, inorder to reduce the risks of rupture for the rim 3.

In the area of the transition zones Z2, the thickness e6 is equal to anintermediate thickness e6int between the minimum thickness e6min and themaximum thickness e6max. For each transition zone Z2, the intermediatethickness e6int, in a particular embodiment, varies progressively alongthe circumference of the rim 3, between the intermediate zone Z1 and therespective transmission zone Z3 a 1, Z3 a 2, Z3 b 1 adjacent thetransition zone Z2.

Notable is an outer surface S3 of the rim 3, located outside of theinner volume V and defined by the bridge 6 and by the portions of theflanges 5 a and 5 b located between the bridge 6 and the brakingsurfaces S5 a and S5 b. In the illustrated embodiment, the outer surfaceS3 is associated, i.e., in one piece, therewith. In the radial plane P4of the rim 3, noted is the radius of curvature R6 of an outer surface S6of the bridge 6, which is oriented so as to be opposite the axis ofrotation X and is outside of the volume V. The outer surface S6 has acenter of curvature C6. The bridge 6 is not exactly in the form of anarc of a circle. Therefore, the radius of curvature R6 is variable. Theradius of curvature R6 is measured on a median zone Z6 of the bridge 6,which has a transverse width measured perpendicular to the plane P andequal to 10 mm.

In the median zone Z6, the radius of curvature R6 is less than 15 mm or,in a particular embodiment, less than 10 mm. For example, the radius R6is equal to 8.0 mm. A large radius of curvature R6 would degrade theaerodynamics of the rim 3. The small radius of curvature R6 provides therim 3 with optimized aerodynamics.

As shown in FIG. 2, the height h5 of the braking surfaces S5 a, S5 b isgreater in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1than in the area of the intermediate zones Z1. As explained below, thisconstitutes an audible indicator of worn-out pads 81.

The rectangular zone Z8 of the rim 3, shown in FIG. 2, represents thezone of contact between the surface S8 of the pad 81 and the rim 3during braking, when the pad 81 is not worn out, or is slightly wornout. This configuration is shown in FIG. 7. Over the entirecircumference of the rim 3, the contact between the pad 81 and the rim 3occurs only in the area of the a respective braking surface S5 a, S5 b,and the friction surface S8 of the pad 81 does not cover the outersurface S3 of the rim 3, which is set back toward the median plane Pwith respect to each respective braking surface S5 a, S5 b.

The zone Z8′ of the rim 3 represents the contact zone between thefriction surface S8 of the pad 81 and the rim 3 during braking, when thepad 81 is worn out. This configuration is shown in FIG. 9. Due to theflared shape of the pad 81, the surface of the zone Z8′ is larger thanthe surface of the zone Z8. When a pad 81 is worn out and in contactwith the rim 3 above the outer surface S3, in the area of theintermediate zones Z1, a portion of the friction surface S8 of the pad81 overlaps in the area of the braking surfaces S5 a, S5 b. In the areaof the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, the contact betweenthe pad 81 and the rim 3 occurs entirely, or almost entirely, on thebraking surfaces S5 a, S5 b. Thus, when the pad 81 is worn out, due tothe height difference Δh between the intermediate zones Z1 and thetransmission zones, Z3 a 1, Z3 a 2, Z3 b 1, the portion of the frictionsurface S8 of the pads 81 which, during braking, is in contact with therim 3 in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, islarger than in the area of the intermediate zones Z1.

During braking, the wheel 1 turns and the pad 81 rubs on the brakingsurfaces S5 a, S5 b. When the pad 81 is not worn out, the sound producedby this friction is constant throughout the braking. Conversely, whenthe pad 81 is worn out, the sound produced by the friction changes whenthe pad 81 rubs in the area of the transmission zones Z3 a 1, Z3 a 2, Z3b 1. This difference in sound enables the user to determine, duringbraking, whether the pad 81 is worn out. Indeed, due to the heightdifference Δh, the sound produced by the friction of the pads 81 becomesdiscontinuous if the pads 81 are worn out, and a staccato sound alertsthe user that the pads 81 are worn out.

The width L8 of the pad 81 decreases in a more pronounced manner on theside of the pad 81 turned toward the axis of rotation X and in thevicinity of the support 82 than on the side of the friction surface S8.Due to the sharp variation in the width L8 near the support 82, in thezone of maximum wear of the pad 81, the sound signal is emitted quitesuddenly, thereby making it easy to detect. This sharp variation in thewidth L8 occurs on the side of the axis of rotation X because this zonerubs on the portion of the braking surfaces S5 a, S5 b having the heightdifferences Δh that is useful for the detection of wear. Alternatively,the pad 81 is symmetrical and its width L8 decreases in a morepronounced manner in the vicinity of the support 82, on the side of thepad 82 turned toward the axis of rotation X and on the side of the pad82 turned toward the tire.

The following description relates to a method for manufacturing the rim3, shown in FIG. 10, which proceeds successively from 1001 to 1008.

During extrusion 1001, a rectilinear section 30, whose transverse crosssection is shown in FIG. 6, is made by extruding or spinning a metalalloy, such as an aluminum alloy, for example. The cross section of thesection 30 is similar to that of the rim 3 and comprises two flanges 5a, 5 b and an arcuate bridge connecting the flanges 5 a, 5 b. Atransverse wall 7, generally perpendicular to the flanges 5 a, 5 b,connects the flanges 5 a, 5 b to one another. On the side opposite thebridge, the flanges 5 a, 5 b are each provided with an L-shaped hook 51a, 51 b.

The bridge of the section 30 has a thickness e60, shown in FIG. 6,measured along the radial direction R in the median plane P,perpendicular to the longitudinal axis X30 of the section.

The outer surface S60 of the bridge of the section 30 has a center ofcurvature C0 and a radius of curvature R0, measured over a zone Z60 10mm wide. The radius R0 is greater than the radius R6 of the rim 3. Theradius R0 is greater than 20 mm.

During bending 1002, the portion of the section 30 is bent to form aplurality of circular helical coils, for example by means of a rollbender. For example, three coils are formed from the section 30 whichthen has a length equivalent to about three times the circumference ofthe rim 3.

During cutting 1003, the coils are cut to obtain a plurality of ringshaving the same perimeter as the rim 3.

To avoid the appearance of defects in the material of the section 30during the extrusion, the walls of the section 30 should be sufficientlythick. In addition, when the walls of the section 30 are too thin, thesection 30 may buckle during bending, and undesired bends may form inthe area of the bridge during bending. To prevent these conditions, thethickness e60 of the bridge of the section 30 is greater than 1.6 mm or,in a particular embodiment, greater than 1.9 mm.

During assembly 1004, the ends of the ring obtained during the cutting1003 are butt-joined and affixed to one another, for example by welding.Alternatively, the ends can be connected by sleeving, by inserting anattached element in the inner volume V at respective ones of the ends ofthe ring.

The thickness e60 of the section 30 is sufficiently great to produce asolid weld. If the thickness e60 is too small, the weld becomes verydifficult to achieve and may break.

During drilling 1005, the valve hole 43 is made, for example by means ofa drill.

During flow drilling 1006, the holes 41 and bushings 42 for fasteningthe spokes 4 a 1, 4 a 2, 4 b 1 are made simultaneously by flow drilling,that is to say, by drilling without cutting. To do this, a flow drillbit operating on the outer surface of the bridge, in the direction ofthe transverse wall 7, is used to create the bushings 42. The initialthickness e60 of the bridge is sufficient for the bushing 42 to havegood mechanical strength. Indeed, the quantity of material flowing backis relatively large, which makes it possible to obtain a sufficientlythick bushing. The valve hole 43 forms an angular reference mark formaking the holes 41 and the bushings 42, as well as for carrying out thefollowing parts of the method.

The radius R0 is relatively large, which prevents the flow drill bitfrom slipping on the bridge, especially when a drill bushing is not usedto hold it.

During machining 1007, the outer surface S3 of the rim 3 is machined inits entirety over the entire periphery of the rim 3, that is to say,over 360° and over each zone Z1, Z2, Z3 a 1, Z3 a 2, and Z3 b 1. Forexample, one can use a concave milling cutter 100, shown in FIG. 17,which has a generally U-shaped profile or cutting surface S100, andwhich makes it possible to machine the entire outer surface S3 in asingle pass, concurrently in the area of the bridge and in the area ofthe flanges 5 a, 5 b. Alternatively, a convex milling cutter, a roundbur, or any other appropriate cutting tool, can be used.

During a complementary machining portion of the method, the brakingsurfaces S5 a and S5 b are machined, for example by means of an endmill.

Thus, the only machined surfaces of the rim 3 are the outer surface S3and the braking surfaces S5 a and S5 b. The inner surface S7 a of thetransverse wall 7, which demarcates the volume V, as well as surfacesS′6a, S′5 a, S′Sb of the bridge and of the flanges 5 a, 5 b whichdemarcate the volume V, are not machined. Similarly, the outer surfaceS7 b of the transverse wall 7, which is located outside of the volume Vand includes the locating member 71, is not machined. In other words,the only surface of the rim 3 which is machined is an “extended” outersurface that includes the outer surface S3 and the braking surfaces S5 aand S5 b.

In the case in which the ends of the section 30 are welded together, themachining 1007 makes it possible to trim the weld and create a smoothsurface finish over the entire circumference of the rim 3. The weld isthen no longer visible, thereby improving the aesthetics of the rim 3.It is not necessary to machine the weld seam subsequently, thus reducingthe number of manufacturing steps.

When the rim 3 is machined with a concave milling cutter, the curvatureof the outer surface S3 is continuous and does not form a ridge. Inother words, the trace of the outer surface S3 in a radial plane is acurve whose derivative is continuous. Therefore, the aerodynamics of thewheel are improved.

The machining is relatively simple as it can be carried out with asingle-axis milling machine, by rotating the rim 3 about the axis X inrelation to the tool and by radially translating the tool, whichsimultaneously creates the variations in the thickness e6 of the zonesZ1, Z2, Z3 a 1, Z3 a 2, Z3 b 1 and the variations in the height h5. Thismakes it possible to reduce the cycle time to less than 1 minute. Thus,the manufacturing cost of the rim 3 is reduced.

Because flow drilling is performed prior to machining, the trimming ofthe holes 41 and 43 occurs automatically during the machining 1007. Itis not necessary to perform additional trimming for the holes 41 and 43.

In threading 1008, the inner surface of each of the bushings 42 isthreaded to form a thread for threaded engagement of the heads 40 of thespokes 4 a 1, 4 a 2, 4 b 1.

During machining, the removed material thickness in the area of thebridge is more or less substantial, depending upon the machined zone Z1,Z2, Z3 a 1, Z3 a 2, Z3 b 1. The transmission zones Z3 a 1, Z3 a 2, Z3 b1 retain a relatively substantial thickness e6max. Between the spokes,the thickness e6min of the intermediate zones Z1 is finer. Thetransition zones Z2 have a thickness e6int that varies progressively.

The machined material thickness and the location of the holes 41 may beadjusted according to several parameters, such as the number of spokesof the wheel 1, the weight of the user, the type of brake (shoe or diskbrake), the type of practice (track biking, cross biking, mountainbiking, etc.), and the type of spokes, for example. Thus, a rim adaptedto the desired application can be made from the same section 30 bychanging the manufacturing parameters, in particular the machiningrange.

In a supplemental machining portion 1009 of the method, the brakingsurfaces S5 a and S5 b are machined, for example, by turning or with anend mill.

Notable is a ratio A, whose denominator is the thickness e60, and whosenumerator is the maximum thickness e6max. The ratio A is less than 90%.

In the embodiment mentioned above, for example, the ratio A is equal to87.5% (2.1/2.4).

Alternatively, the variation of the thickness e6 between the minimumthickness e6min and the maximum thickness e6max is not progressive, suchthat the outer surface S3 of the rim 3 has, at least in the area of thebridge, a ridge or break that is generally oriented parallel to the axisX. In this case, in the area of the transition zones Z2, theintermediate thickness e6int has a discontinuous variation along thecircumference of the rim 3, between the intermediate zone Z1 and thetransmission zone Z3 a 1, Z3 a 2, and Z3 b 1 adjacent the transitionzone Z2.

The rim 3 is part of a rear cycle wheel 1, but the invention alsoapplies to front wheels. The invention also applies to rims havingvaried numbers of spokes and of various types.

Alternatively, during the flow drilling 1006, boring with materialremoval is used, instead of flow drilling. In such a case, the rim iscut out to form the holes 41. Bushes can then be fixed in the holes 41for fastening the spokes 4 a 1, 4 a 2, 4 b to the rim 3. Flow drilling,which consists of drilling without material removal, and drilling withmaterial removal, are considered two alternative methods of drilling.

The milling cutter 100 shown in FIG. 17 has a concave profile with acontinuous curvature. In an alternative, however, the concave profilehas at least one ridge oriented along a circumferential direction, forexample between the bridge and a flange 5 a or 5 b.

FIGS. 11 to 15 show a rim 103 according to a second embodiment of theinvention. In the second embodiment, the elements similar to those ofthe first embodiment are not described in detail. The elements of therim 103 similar to those of the rim 3 are designated by the samereference numerals increased by 100.

The rim 103 is made from an asymmetrical section to improve thedistribution of the forces transmitted between the rim 103 and thespokes 4 a 1, 4 a 2, 4 b 1, which do not extend exactly along the radialdirection R and do not all have the same orientation in relation to theplane P.

The rim 103 is made using a method similar to that described above. Itis possible to machine the rim 103 from an asymmetrical section, with amilling cutter having a concave profile, whose axis of rotation isinclined relative to the plane P.

The transverse cross section of the rim 103 has the shape of a hollowbox and comprises two flanges 105 a, 105 b and a bridge 106. Atransverse wall 107 connects the flanges 105 a, 105 b to one another,opposite the bridge 106. On the side opposite the bridge 106, theflanges 105 a, 105 b are each provided with an L-shaped hook 151 a, 151b, provided for fastening a tire, not shown, to the rim 103.

Holes 141 connected to bushings 142 are made in the bridge 106.

Similar to the rim 3, the rim 103 is divided into a plurality of zonesZ1, Z2, Z3 a 1, Z3 a 2, Z3 b 1, which divide the circumference of therim 103 into a plurality of angular sectors. As shown in FIGS. 12 to 15,the thickness e106 of the bridge 106 varies, depending upon the zone Z1,Z2, Z3 a 1, Z3 a 2, Z3 b 1 of the rim 103, in a manner similar to therim 3 of the first embodiment.

The thickness e106 varies between a maximum thickness e106max, in thearea of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, and a minimumthickness e106min, in the area of the intermediate zones Z1. In the areaof the transition zones Z2, the thickness e106 is equal to anintermediate thickness between the minimum thickness e106min and themaximum thickness e106max.

The maximum thickness el06max of the transmission zones Z3 a 1 of thedriving spokes 4 a 2 is greater than the maximum thickness e106max ofthe transmission zones Z3 a 2 of the non-driving spokes 4 a 1. Thethickness e106max of the transmission zones Z3 b 1 of the spokes 4 b 1of the driven spoke set 4 b is less than the thickness e106max of thespokes 4 a 1, 4 a 2 of the driving spoke set 4 a.

FIG. 16 shows a rim 203 according to a third embodiment of theinvention. In the third embodiment, the elements similar to those of thefirst embodiment are not described in detail. The elements of the rim203 similar to those of the rim 3 are designated by the same referencenumerals increased by 200.

The rim 203 is made using a method similar to that described above anddiffers from the rims 3 and 103 in that it is part of a disc brakewheel.

The transverse cross section of the rim 203 has the shape of a hollowbox and comprises two flanges 205 a, 205 b and a bridge 206. Atransverse wall 207 connects the flanges 205 a, 205 b to one another,opposite the bridge 206. On the side opposite the bridge 206, theflanges 205 a, 205 b are each provided with an L-shaped hook 251 a, 251b, provided for fastening a tire, not shown, to the rim 203.

The rim 203 has an outer surface S203, which is oriented outward of therim 203 and is defined by the bridge 206 and by the flanges 205 a, 205b, up to the free ends of the hooks 251 a, 251 b. In radial crosssection, the outer surface S203 is curved over its entire length. Unlikethe rims 3 and 103, the outer surface S203 does not include a planarzone provided to cooperate with a brake pad.

In FIG. 16, a hatched zone M1 corresponds to the transverse crosssection of the rim 203, in the area of the intermediate zones Z1 inwhich the thickness e206 of the bridge 206 is equal to a minimumthickness e206min.

The joining of the hatched zone M1 with a hatched zone M2 corresponds tothe transverse cross section of the rim 203, in the area of thetransmission zones Z3 a 1, Z3 a 2, or Z3 a 3. The maximum thicknesse206max is measured in the area of the transmission zones Z3 a 1, Z3 a2, Z3 a 3, on the joining of the zones M1 and M2. The hatched zone M2corresponds to the excess material thickness between the intermediatezones Z1 and the transmission zones Z3 a 1, Z3 a 2, or Z3 a 3 andrepresents the difference between the minimum thickness e206min and themaximum thickness e206max.

The joining of the hatched zones M1 and M2 with a hatched zone M3corresponds to the transverse cross section of a section 230 from whichthe rim 203 is manufactured. Notable is the thickness e260 of the bridge206 of the section 230. The thickness e260 is greater than the maximumthickness e206max.

The following description provides examples of various thicknesses e206and e260 of the rim 203 and of the section 230. These thicknesses canalso be selected for the rims 3 and 103.

The thickness e260 of the bridge 206 of the non-machined section 230,measured at the end of the extrusion 1001 and prior to the bending 1002,is equal to 2.5 mm.

At the end of machining 1007, the maximum thickness e206max, measured inthe area of the transmission zones Z3 a 2 in which the driving spokes 4a 2 are fastened, is equal to 2.1 mm. These transmission zones Z3 a 2are the most mechanically biased in view of the fastening of the drivingspokes 4 a 2. Considering the rim 203 at the end of its manufacture, thethickness e206max in the area of the transmission zones Z3 a 2 is thegreatest thickness e206 of the bridge 206 over the entire circumferenceof the rim 203.

The maximum thickness e206max, measured in the area of the transmissionzones Z3 a 1 in which the non-driving spokes 4 a 1 are fastened, isequal to 1.9 mm.

The maximum thickness e206max, measured in the area of the transmissionzones Z3 b 1 in which the spokes 4 b 1 of the driven spoke set 4 b arefastened, is equal to 1.7 mm. The spokes 4 b 1, located opposite thefree wheel mechanism 22 of the hub 2, do not transmit torque and thusare not very biased, which explains the relatively small value of thethickness e206max in the zones Z3 b 1.

In the area of the intermediate zones Z1, the minimum thickness e206minis equal to 0.65 mm.

In this example, the greatest difference between the thicknesses e206maxand e206min, considered in the area of the transmission zones Z3 a 2 ofthe driving spokes 4 a 2, is equal to 1.25 mm.

ε206 is the removed material thickness at the bridge 206, at the end ofthe machining 1007, measured along the radial direction R, in the planeP and perpendicular to the axis X. The thickness a06 is equal to thedifference between the thickness e260 of the bridge 206 of the section230 and the thickness e206 of the bridge 206 of the rim 203. The removedmaterial thickness ε206 varies as a function of the zone Z3 a 1, Z3 a 2,Z3 b 1, Z2, or Z1 considered. The maximum removed material thicknessε206max is reached in the area of the intermediate zones Z1, in which itis equal to 1.45 mm. The minimum removed material thickness ε206min isreached in the area of the transmission zones E3 a 2 of the drivingspokes 4 a 2, in which it is equal to 0.2 mm.

During the machining 1007, the minimum removed material thicknessE206min selected must be sufficiently substantial in order for themachining to eliminate the asperities generated during the extrusion andbending of the section 230. In a particular embodiment, the minimumremoved material thickness E206min is greater than 0.1 mm or, inspecific case, greater than 0.3 mm.

In addition, during the machining 1007, the depth-of-cut selected shouldbe sufficiently small to ensure complete continuity of the cut and toguarantee a smooth surface finish. In one embodiment, the cutting depthcan be less than 0.4 mm; in another embodiment, a cutting depth of lessthan 0.2 mm can be selected.

FIGS. 18-21 show a rim 303 and a section 330 consistent with a fourthembodiment of the invention and forming part of a disc brake wheel. Inthe fourth embodiment, the elements similar to those of the firstembodiment are not described in detail. The elements of the rim 303 andof the section 330 similar to those of the rim 3 and of the section 30according to the first embodiment are designated by the same referencenumerals increased by 300.

The transverse cross section of the rim 303 has the shape of a hollowbox and comprises two lateral flanges 305 a and 305 b and a bridge 306.A transverse wall 307 connects the flanges 305 a, 305 b to one another,opposite the bridge 306. On the side opposite the bridge 306, theflanges 305 a, 305 b are each provided with an L-shaped hook 351 a, 351b, provided for fastening a tire, not shown, to the rim 303.

The rim 303 is made using a method that is generally similar to thatdescribed above and differs from the rims 3, 103, and 203 in that onlythe bridge 306 of the rim 303 is machined during the machining 1007.Thus, the lateral flanges 305 a, 305 b are not machined.

The rim 303 has an outer surface S303 oriented outward of the rim 303and defined by the bridge 303 and by all of the flanges 351 a, 351 b, upto the free end of the hooks 251 a, 351 b.

In FIGS. 20 and 21, a hatched zone M10 corresponds to the transversecross section of the rim 303, in the area of the intermediate zones Z1,in which the thickness e306 of the bridge 306 is equal to a minimumthickness e306min.

The joining of the hatched zone M10 with a hatched zone M20 correspondsto the transverse cross section of the rim 303, in the area of thetransmission zones Z3 b 1 in which the spokes 4 b 1 comprised in thedriven spoke set 4 b are fastened. Notable is a maximum thicknesse′306max measured in the area of the transmission zones Z3 b 1, on thejoining of the zones M10 and M20. The hatched zone M20 thus correspondsto the excess material thickness between the intermediate zones Z1 andthe transmission zones Z3 b 1 and represents the difference between theminimum thickness e306min and the maximum thickness e′306max.

The joining of the hatched zones M10 and M20 with a hatched zone M30corresponds to the transverse cross section of the rim 303, in the areaof the transmission zones Z3 a 1, Z3 a 2, in which the spokes 4 a 1, 4 a2 comprised in the driving spoke set 4 a are fastened. Notable is amaximum thickness e306max measured in the area of the transmission zonesZ3 a 1, Z3 a 2, on the joining of the zones M10, M20, and M30. Thehatched zone M30 thus corresponds to the excess material thicknessbetween the transmission zones Z3 b 1 in which the spokes 4 b 1 of thedriven spoke set 4 b are fastened and the transmission zones Z3 a 1, Z3a 2 in which the spokes 4 a 1, 4 a 2 of the driving spoke set 4 a arefastened. The hatched zone M30 thus represents the difference betweenthe maximum thickness e′306max and the maximum thickness e306max.

The joining of the hatched zones M10, M20, M30, with a hatched zone M40corresponds to the transverse cross section of the section 330 fromwhich the rim 303 is made. Notable is the thickness e360 of the bridge306 of the section 330. The thickness e360 is greater than the maximumthickness e306max.

The thicknesses e306 and e360 of the rim 303 and of the section 330 maybe selected to be equal to the thicknesses e206 and e230 of the rim 203and of the section 230 according to the third embodiment.

The following description relates to a fifth embodiment of theinvention, in which a rim, not shown, is made from the section 330 ofFIG. 18.

The method for manufacturing this rim is generally similar to that forthe rim 303. However, in the machining 1007, only a median zone Z306 ofthe outer surface of the bridge 306 is machined, over the entirecircumference of the rim. Thus, the bridge 306 is not machined in itsentirety. The median zone Z306 has a transverse width L306, measuredperpendicular to the median plane P and greater than or equal to 4 mm.Thus, the bridge 306 is machined in the vicinity of all of the zones ofattachment of the spokes 4 a 1, 4 a 2, 4 b 1, in the locations in whichthe mechanical stresses are the most substantial. Machining the bridge306 only in the area of the median zone Z6 delays the appearance ofcracks that might be initiated when the rim is used and subject toconditions causing fatigue. For example, it is possible to machine theintermediate zones Z1 only, or both the intermediate zones Z1 and thetransition zones Z2.

The known prior art methods for manufacturing rims have systematicallysought to reduce the thickness of the section to a maximum. Conversely,the invention deliberately provides a thickness e60 of the bridge 6 ofthe section that is relatively substantial, greater than the maximumthickness e6max of the bridge 6, considered at the end of themanufacture of the rim 3 and over the entire circumference of the rim 3,and subsequently to machine the entire circumference of the rim 3.

In the context of the invention, the various embodiments described abovecan be combined with one another, at least partially.

At least because the invention is disclosed herein in a manner thatenables one to make and use it, by virtue of the disclosure ofparticular exemplary embodiments of the invention, the invention can bepracticed in the absence of any additional element or additionalstructure that is not specifically disclosed herein.

1. A rim for a cycle wheel, said rim comprising: two lateral flangeslocated on opposite respective sides of a median plane of the rim andeach of the two lateral flanges comprising an outer surface facing awayfrom the median plane; a bridge connecting the flanges to one anotherand comprising an outer surface facing an axis of rotation of the wheel;the two lateral flanges and the bridge forming a U-shaped radial crosssection; at least one machined middle zone of the outer surface of thebridge; the machined middle zone having a transverse width, measuredperpendicular to the median plane, greater than 4 mm; the machinedmiddle zone extending over an entirety of a circumference of the rim. 2.A rim according to claim 1, wherein: an entirety of the outer surface ofthe bridge is a machined outer surface over the entirety of thecircumference of the rim.
 3. A rim according to claim 2, furthercomprising: a rim outer surface facing outward of the rim and comprisingboth the outer surface of the bridge and at least respective portions ofthe outer surfaces of the flanges; the respective portions of the outersurfaces of the flanges being connected to the outer surface of thebridge; the rim outer surface being a machined outer surface over anentirety of the rim outer surface and over the entirety of the rim.
 4. Arim according to claim 3, wherein: the rim outer surface includes anentirety of the outer surfaces of the flanges.
 5. A rim according toclaim 1, wherein: the rim comprises a plurality of zones dividing thecircumference of the rim into angular sectors, the zones comprising:transmission zones located around the zones of attachment of the spokesof the wheel; and intermediate zones located between the transmissionzones; in an area of the transmission zones, the bridge having athickness, measured in the median plane, equal to a maximum thickness;in an area of the intermediate zones, the bridge having a thicknessequal to a minimum thickness less than the maximum thickness.
 6. A rimaccording to claim 5, wherein: the maximum thickness of the bridge isgreater than 1.6 mm.
 7. A rim according to claim 5, wherein: the maximumthickness of the bridge is greater than 2.0 mm.
 8. A rim according toclaim 5, wherein: the minimum thickness of the bridge is less than 0.8mm.
 9. A rim according to claim 5, wherein: the minimum thickness of thebridge is less than 0.65 mm.
 10. A rim according to claim 5, wherein:the plurality of zones further includes transition zones each locatedbetween a transmission zone and an intermediate zone; in an area of thetransition zones, the thickness of the bridge is equal to anintermediate thickness which varies progressively between the minimumthickness and the maximum thickness of the bridge.
 11. A rim accordingto claim 1, wherein: in a radial cross section of the rim, a radius ofcurvature of the bridge is less than 15 mm.
 12. A rim according to claim1, wherein: in a radial cross section of the rim, a radius of curvatureof the bridge is less than 10 mm.
 13. A rim according to claim 1,wherein: the bridge comprises internally threaded cylindrical bushingsfor fastening spokes of the wheel; the bushings are made unitary withthe rim.
 14. A rim according to claim 5, wherein: the flanges eachdefine a planar braking surface, structured and arranged to cooperatewith a brake pad; a height of at least one of the braking surfaces,measured radially, is greater in the area of the transmission zones thanin the area of the intermediate zones.
 15. A wheel comprising: a rim; ahub; a plurality of spokes extending between the rim and the hub; therim comprising: two lateral flanges located on opposite respective sidesof a median plane of the rim and each of the two lateral flangescomprising an outer surface facing away from the median plane; a bridgeconnecting the flanges to one another and comprising an outer surfacefacing an axis of rotation of the wheel; the two lateral flanges and thebridge forming a U-shaped radial cross section; at least one machinedmiddle zone of the outer surface of the bridge; the machined middle zonehaving a transverse width, measured perpendicular to the median plane,greater than 4 mm; the machined middle zone extending over an entiretyof a circumference of the rim.
 16. A method for manufacturing a rim fora cycle wheel, the method comprising: extruding a rectilinear section,the section comprising: two lateral flanges located on respectiveopposite sides of a median plane of the rim and each of the two lateralflanges comprising an outer surface facing away from the median plane; abridge connecting the flanges to one another and comprising an outersurface facing an axis of rotation of the wheel; bending the section toform at least one hoop having two ends; assembling the ends of the hoopof the section to one another to define a circumference; drilling holesthrough the bridge for fastening the spokes of the wheel; after thedrilling, machining at least one median zone of the outer surface of thebridge over an entirety of the circumference of the rim, the median zonehaving a transverse width of greater than 4 mm measured perpendicular tothe median plane of the rim.
 17. A method according to claim 16,wherein: said machining comprises machining the outer surface of thebridge in its entirety over an entirety of the circumference of the rim.18. A method according to claim 16, wherein: during said machining,machining an entirety of a rim outer surface over the entirety of thecircumference of the rim, the rim outer surface facing outward of therim and comprising: the outer surface of the bridge; and at leastrespective portions of the outer surfaces of the flanges connected tothe outer surface of the bridge.
 19. A method according to claim 18,wherein: said machining comprises machining using of a milling cutterhaving a concave profile and enabling the bridge and at least therespective portions of the flanges adjoining the bridge to be machinedsimultaneously in a radial plane.
 20. A method according to claim 16,wherein: at the end of said extruding, a radius of curvature of theouter surface of the bridge of the section, measured in a radial planeof the rim, is greater than 20 mm; and at the end said machining, aradius of curvature of the outer surface of the bridge of the rim isless than 15 mm.
 21. A method according to claim 16, wherein: at the endof said extruding, a radius of curvature of the outer surface of thebridge of the section, measured in a radial plane of the rim, is greaterthan 20 mm; and at the end said machining, a radius of curvature of theouter surface of the bridge of the rim is less than 10 mm.
 22. A methodaccording to claim 16, wherein: at the end of said extruding, athickness of the bridge of the section is greater than 1.6 mm.
 23. Amethod according to claim 16, wherein: at the end of said extruding, athickness of the bridge of the section is greater than 1.9 mm.
 24. Amethod according to claim 16, wherein: a ratio is less than 90%, saidratio comprising: a denominator being a thickness of the bridge of thesection at the end of said extruding; and a numerator being a thicknessof the bridge of the rim at the end of said machining.
 25. A methodaccording to claim 16, wherein: during said drilling, holes and bushingsfor fastening the spokes are made simultaneously by flow drilling thebridge without cutting.
 26. A method according to claim 16, wherein: amachining minimum thickness, equal to the difference between thethickness of the bridge of the section, measured at the end of saidextruding, and the minimum thickness of the bridge of the rim, measuredat the end of said machining and considered over an entirety of thecircumference of the rim, is greater than 0.1 mm.
 27. A method accordingto claim 16, wherein: a machining minimum thickness, equal to thedifference between the thickness of the bridge of the section, measuredat the end of said extruding, and the minimum thickness of the bridge ofthe rim, measured at the end of said machining and considered over anentirety of the circumference of the rim, is greater than 0.3 mm.